错误演示

#include <stdio.h>
int main()
{
    float pai = 3.141592;
    int r, zc, mj;
    zc = 2 * pai * r; //没有给zc mj r 赋初始值，故不能直接放在前面
    mj = pai * r * r;  //定义的zc和mj要在scanf抓取地址给其r zc mj 赋值之后再进行运算 应该放到scanf后面
    printf("输入半径\n: ");
    scanf("%d", &r);
    printf("以%d为半径的圆面积和周长分别是%d和%d", r, mj, zc);

}

正确代码

#include <stdio.h>
int main()
{
    float pai = 3.141592;
    int r, zc, mj;
    printf("输入半径\n: ");
    scanf("%d", &r);
    zc = 2 * pai * r;  //此位置
    mj = pai * r * r;  //此位置
    printf("以%d为半径的圆面积和周长分别是%d和%d", r, mj, zc);

}